1. Field of the Invention
The present invention relates to a device for supporting an overhang type slidable pinion shaft of an electric motor for starting an engine.
2. Description of the Prior Art
A typical conventional device for supporting an overhang type slidable pinion shaft of an electric motor for starting an engine will first be explained with reference to FIGS. 4 and 5. FIG. 4 is a fragmentary sectional view showing an essential part of a starting motor, and FIG. 5 shows a bearing employed in the motor shown in FIG. 1. In the figures, the reference numeral 1 denotes a magnetic switch, 2 a plunger, 3 a lever, 4 a shaft, 5 a stopper, 6 a clutch, 7 a pinion shaft, 7a a pinion, 8 a bracket, and 9 a ball bearing press-fitted into the bracket 8, the bearing 9 consisting of an inner ring 9a, balls 9b, an outer ring 9c and a retainer 9d. The numeral 10 denotes a ring gear.
In operation, when a voltage is applied to the magnetic switch 1 to draw the plunger 2 into the body of the switch 1, the clutch 6 is shifted forward (rightward as viewed in FIG. 4) through the lever 3, thus causing the pinion shaft 7 to move forward while rotating with the outer peripheral portion thereof which is supported by the ball bearing 9. In this way, the pinion 7a is meshed with the ring gear 10 of the associated engine.
The above-described conventional device for supporting an overhang type slidable pinion shaft of an engine starting motor suffers, however, from the following problem. Namely, in order to ensure smooth sliding movement of the pinion shaft 7, a film of oil must be constantly present in the area between the outer peripheral surface of the sliding portion of the pinion shaft 7 and the inner peripheral surface of the inner ring 9a of the ball bearing 9. If the oil film should disappear during use, the pinion shaft 7 will lose its ability to slide smoothly and may fail to engage with the ring gear 10. In such a case, it would be impossible to start the engine.